Create fixed sun presets (Sunrise, Midday, Sunset, Midnight) and make them accessible via World->Sun menu and keyboard shortcuts.
See spec page 7.
- Sunrise: none
- Midday: Ctrl+Shift+Y
- Sunset: Ctrl+Shift+N
- Midnight: none
The presets will most likely be copies of the existing presets: "A-6AM", "A-12PM", "A-6PM", "A-12AM", respectively
(although I'm not sure about midday).